1. Field of the Invention
This invention relates to a loop-type binder for punched document sheets, consisting of a back cover onto which elastic tongues are mounted for filing sheets and of a front cover with eyelets opposite these tongues into which the tongues engage and in which the tongues are retained using a stopper.
2. Description of the Related Art
Such binders for filing sheets of paper are known, for example, from German patent DE 195 27 872 A1. The tongues are locked into place on the back cover by means of a base comprising a latch element. The tongue end connected to the base has the design of a laminated spring, and the tongue comprises a reduction in width (waist) in its center section and a bulge on its back that faces the back cover. This design is to ensure that the tongues form a ring when the binder is open and are elastically retained in the eyelets so that any sheets filed on them can be turned over conveniently and without being damaged. However, when the binder is closed, this design is to prevent any restoring forces from applying to the front cover which would result in keeping it slightly open.
This problem of restoring forces acting on the covers indeed remains unsolved with known loop-type binders. When the joint between the tongue and the base is thin and the elastic effect on the front cover is low, the curvature required for easy turning over sheets is not fully developed, and document sheets may got caught in the joining area between the base and the tongue or even be damaged. If the tongue or some of its parts are not stiff enough, it may also be more difficult to file the punched paper on them. Finally, a weak joint can be damaged after long-term use. Another disadvantage of the known binders with tongues is that the stoppers provided for preventing the tongues from sliding out may damage the documents despite their relatively small height, especially when the closed binder is exposed to pressure that presses the stoppers into the sheets.
It is the problem of this invention to provide a loop-type binder as described above with tongues whose design ensures convenient and safe handling of the binder and the document sheets stored in it.
The major idea of the invention is that the tongue increases in thickness from its root to its tip and that an indent or slope of a limited length is molded into the thicker tongue area that gradually inclines towards the tip and at its end comprises a stopper surface that is molded into the tongue. The joining area between the tongue and the base connected to it in one piece has a large radius on the side facing the front cover of the binder while this same area between the tongue surface facing the back cover of the binder and the base is rather small in radius.
The tongue design according to the invention causes the tongues to bend in a well-formed curvature when the binder is open and the tongues are retained in their eyelets so that the document sheets can conveniently be turned over and do not get caught or damaged. When the binder is closed, however, the restoring forces of the tongues that act on the front cover are small, which means that the cover of the loop-type binder will not be lifted. Furthermore, the stopper that is molded into each tongue will not produce any imprints in the document sheets, as protruding stoppers would commonly do. This way of integrating the stopper into the tongue is possible due to the increasing material thickness of the tongue towards the tip. And finally the proposed tongue design has the advantage that the free end of the tongue is particularly deflection resistant, which makes filing new document sheets onto them easy.